The present invention relates to a linear motion device. Linear motion devices of that type are known as bearing rail guides or roller rail guides, or as linear modules.
U.S. Pat. No. 4,744,551 makes known a linear motion device. According to FIG. 1 of U.S. Pat. No. 4 744 551, the linear motion device includes a first assembly in the form of a table 26 which is linearly movable relative to a second assembly in the form of a U-shaped guide rail 12. Two first rolling surfaces 28; 30 which extend in a longitudinal direction are provided on the first assembly, each of which is opposite a second rolling surface 22; 24 on the second assembly. A row of spherical roller-shaped rolling elements 32 that may circulate endlessly in the first assembly is situated between the aforementioned rolling surfaces, as shown in FIG. 5.
The embodiment depicted in FIG. 7 of U.S. Pat. No. 4,744,551 deals with a problem that occurs when the first rolling surface, about which the rolling elements circulate, is very long. The back-up of rolling elements is caused by the fact that the individual rolling elements are not loaded equally, due to production inaccuracies. In turn, this causes the individual rolling elements to slip differently, which results in a non-uniform running speed. As a result of this, the rolling elements bump into one another and prevent one another from rolling. This problem increases continually as the length of the first rolling surfaces increases, until it eventually halts the movement of the first assembly entirely. As a solution to this problem, it is provided in U.S. Pat. No. 4,744,551 that load-carrying rolling surface sections 104; 106, between which a substantially load-free rolling surface section 108 is provided, be situated in the two end regions of the first rolling surfaces. In the load-free rolling surface section, the load and, therefore, the non-uniformity of the load distribution on the rolling elements is very small. Moreover, in the load-free rolling surface section, the rolling elements are displaceable via sliding between the rolling surfaces, thereby preventing the rolling elements from becoming backed up. The load-free section is provided as a single piece on the first rolling surface, and it may be provided, e.g., by grinding back the first rolling surface, which is an expensive procedure, however.
DE 102 37 278 B4 makes known a further linear motion device, in which the first rolling surfaces are provided on separate rolling surface parts which are supported on a first body of the first assembly. The rolling surface parts are manufactured as profiled elements having a substantially constant cross-sectional profile in the form of blanks that are several meters long. Sections of the appropriate length are separated, with no further machining, from these blanks in order to install them into the linear motion device. The body of the first assembly is composed of aluminum, and not of steel as usual, and may therefore be machined in a particularly cost-favorable manner. In all, an extraordinarily cost-favorable linear motion device is attained as a result.